how to stop inpedence rise

[PV Audio 5,000+ posts]

No need to clean up. I was able to follow all of it. I'm working on my PhD in mechanical engineering, specializing in controls... so I may not have enough practical experience, but I can understand "no imaginary parts" just fine. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Side Note: It took me 2 classes and a summer of leisure studying, to finally learn bode plots... and how I got it? By realizing that FRF = "speaker frequency response plots." //content.invisioncic.com/y282845/emoticons/veryhappy.gif.fec4fed33b4a1279cf10bdd45a039dae.gif

I did have a question. When you said "the larger the box, the lower the resonant frequency of the box"... I didn't quite follow you there. Are you referring to box volume's resonance, port's resonance, or the resonance of the combined system (sub-->box volume-->port)?

Stating things, so I can rationalize/internalize:

Box resonance - Since there is more air in the box, the compliance goes up... Thus, the natural frequency drops. This is why manufacturers suggest certain box sizes (0.8, 1.2, etc). They attempt to get the total Q of the sub/box near 0.707 which is "optimally controlling" the woofer.

Side note 1: Does the damping change with box size?

Side note 2: Has anyone designed a box that resonates due to internal volume AND standing waves (caused by the physical lengths)? I wonder if you'd get a significant contribution...//content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

Port resonance - The port adds a complicating factor, because it allows flow between the air excited by the front and back waves. At resonance, it allows a significantly more airflow.

Guess: When you are above resonance frequency, the port adds damping to the system. This is why at higher frequencies, ported boxes don't have much cone movement. Conversely, lower than resonance frequencies will decrease the damping of the system and cause the woofer to overshoot and "get floppy."

----- I'll start from here when I get more time. But I think (with help) we're getting to the bottom of ported box theory. Thanks again, for good explanations.

//content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif You're an ME? You should be teaching me, the EE, about this stuff man. What's going on? //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
Anyway, that was a misspeak, you're right. Yes, I meant the larger the box, the lower the SYSTEM'S resonant frequency. Obviously the larger the box, the lower the box's resonant frequency, but that isn't exactly important nor startling information. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

On your Q discussion, I need to know what you mean when you say compliance: compliance of what? I know very little ME stuff beyond what I know about speakers, and even that is limited, but there are many different compliance values for loudspeakers: Vas, Cms, etc...

Seeing as you're talking about .707, what does a sqrt(2) value of stiffness mean in ME? I haven't the faintest idea, however I do know quite well that 1/sqrt(2) is a very important factor in almost all engineering fields, and since compliance is just 1/stiffness, I'm wondering what that signifies //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Again, what damping are you talking about? Ported boxes naturally damp the cone at the tuning frequency, so I'm not too sure what damping you're talking about: cone, box, or some otherwise electrical damping that I might have missed in the conversation (sigma).

Yes, people have tried and failed since it's impossible to obviously reach theoretical numbers in practical applications. The problem is that it isn't feasible to take into account every single factor that can affect how a speaker responds, so instead, people merely tailor their sound to their tastes but use theory to make the initial design.

Your guess is mostly correct as well. Outside of the sub's passband, you're right, there is little cone movement, however, as you decrease in frequency, the cone movement gets greater until a certain point. At tuning frequency, the cone's movement is actually less than at other frequencies. But you are correct that under tuning frequency, the air in the enclosure can no longer control cone movement effectively and thus your sub can bottom out (which is why it's pretty stupid to test subs just sitting on your carpet if they are not designed to play free-air.

A FANTASTIC treatise on box design is Bullock on Boxes, it's a small book all about ported box design and theory. i just started reading it and am like 5 pages in, and already have learned more from those 5 pages than I have in literally years here listening to second hand accounts and tricks of the trade.

 

[tinmanchris217 10+ year member]

Please excuse any poor wordage... it is, in fact, friday night //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif

1) Compliance - inverse of stiffness (like a spring). More compliance means that something has less resistance to moving. When I talk about air compliance, it means that the air is able to absorb alot of cone force without as much reaction force. High compliance = Floppy(ported). Low compliance = Punchy(sealed)

2) 0.707 is the magic number for Q. It's the 1/2 * sqrt(2)... coming from the formula of 2nd order systems.

w^2 / (1 + 2 * z * w + w^2) ... something like that... if you're an EE it's in one of your text books.

Basic idea is that it's not too overdamped, not too underdamped... Critical damping is generally considered to be optimal response (with nothing else to optimize), since it has low rise time, and fast settling time. Critically damped is the best condition for a sealed woofer, in the perfect environment... but ported has alot more leniency... With either, you can tweak the system to give different response, but ported gives you twice the total output to fiddle with.

3) What books do you(and others) recommend on the subject? I don't have enough reading material on the subject.

 

[PV Audio 5,000+ posts]

Please excuse any poor wordage... it is, in fact, friday night //content.invisioncic.com/y282845/emoticons/tongue.gif.6130eb82179565f6db8d26d6001dcd24.gif
1) Compliance - inverse of stiffness (like a spring). More compliance means that something has less resistance to moving. When I talk about air compliance, it means that the air is able to absorb alot of cone force without as much reaction force. High compliance = Floppy(ported). Low compliance = Punchy(sealed)

2) 0.707 is the magic number for Q. It's the 1/2 * sqrt(2)... coming from the formula of 2nd order systems.

w^2 / (1 + 2 * z * w + w^2) ... something like that... if you're an EE it's in one of your text books.

Basic idea is that it's not too overdamped, not too underdamped... Critical damping is generally considered to be optimal response (with nothing else to optimize), since it has low rise time, and fast settling time. Critically damped is the best condition for a sealed woofer, in the perfect environment... but ported has alot more leniency... With either, you can tweak the system to give different response, but ported gives you twice the total output to fiddle with.

3) What books do you(and others) recommend on the subject? I don't have enough reading material on the subject.

1. Gotcha //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

2. Oh no, I am fully aware of, if not completely brain dead after having sqrt(2) and its inverse (turns out .5*sqrt(2) and 1/sqrt(2) as is taught in EE is the exact same thing) shoved down my throat for the past few years. I am just wondering how it applies to what you were talking about. It's the reference standard number for any quality factor, this is true. I am just wondering how it applies to compliance. I'm not familiar with Q with relation to mechanical systems //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif

3. Loudspeaker Design Cookbook - Vance Dickason

Testing Loudspeakers - Joseph D'Appolito

Master Handbook of Acoustics - Alton Everest

The last two are pretty heavy on the math and science, so if you're looking for a bedtime read, look elsewhere //content.invisioncic.com/y282845/emoticons/laugh.gif.48439b2acf2cfca21620f01e7f77d1e4.gif

 

[tinmanchris217 10+ year member]

good choices. I recently bought Loudspeaker Design Cookbook (after so many people raving about it) and Master Handbook of Acoustics (Amazon popularity). Need to take some time to read them.

I haven't heard of Testing Loudspeakers, but it seems to have alot of info on the formulation and use of T/S parameters. I'll save up, since it's $120. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[PV Audio 5,000+ posts]

LOL 120? Maybe if it's hollowed out and filled with cocaine. It's a 30 dollar book:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=500-030

 

[loudacuratl 10+ year member]

the only way to stop it is to not use your audio haha. impedence rise is always there man

 

[csu87 10+ year member]

the only way to stop it is to not use your audio haha. impedence rise is always there man

not stop, just lower. i might make another box this weekend and try that, or ill just pick up another amp. then impedence rise wont bother me so much

 

[loudacuratl 10+ year member]

oh ok. well from wat i have experienced..... cleaner power... a smother box.. and correct tunign will lower it.

 

[tinmanchris217 10+ year member]

Alright, PV. Partsexpress continues to be an awesome one-stop shop. $30 it is... but I still have to read the books in the library before buying more. Otherwise it's an endless cycle. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Next on the list though. Thx for a useful reference.

 

[PV Audio 5,000+ posts]

My man //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[tinmanchris217 10+ year member]

So in the quest for supreme knowledge, I wanted to post the list of impedance sources (according to the loudspeaker design cookbook):

1) DC resistance of the coil and tinsels

2) Real part of the voice coil inductance

3) Imaginary part of the voice coil inductance

4) "Inductance" of the moving mass (cone, dust cap, coil, former, surround, spider)

5) "Capacitance" of the compliance/stiffness of the woofer (suspension, cone, air)

6) "Resistance" of the damping of the woofer (spider, surround)

7) Impedance due to sound waves in the box's air

8) Impedance due to sound waves in the car's air

In an impedance curve, the impedance grows steadily as a woofer goes to higher frequencies, and generally has a peak at Fs.

Fs - Speaker's free air resonant frequency. It is attributed to 4) and 5) (mass and compliance), mostly.

1), 2), and 3) are coil related, while 4), 5), and 6) are soft parts related. To change any of these would require a recone, or a different woofer.

1), 2), and 3) change with different voice coil configurations. This is why the T/S specs are slightly different for different coils in the same woofer. Changing coils will change the way the driver uses the available BL. Generally the higher ohm woofer will have a higher Fs (1 or 2 Hz), lower Qms (-5%), and dramatically higher Qes (10%).

Assuming you like your woofer and coil configuration, and only want to change the box, what are effective ways to decrease the impedance caused by 7) and 8) ??

 

[Crownvicon28s 10+ year member]

So in the quest for supreme knowledge, I wanted to post the list of impedance sources (according to the loudspeaker design cookbook):
1) DC resistance of the coil and tinsels

2) Real part of the voice coil inductance

3) Imaginary part of the voice coil inductance

4) "Inductance" of the moving mass (cone, dust cap, coil, former, surround, spider)

5) "Capacitance" of the compliance/stiffness of the woofer (suspension, cone, air)

6) "Resistance" of the damping of the woofer (spider, surround)

7) Impedance due to sound waves in the box's air

8) Impedance due to sound waves in the car's air

In an impedance curve, the impedance grows steadily as a woofer goes to higher frequencies, and generally has a peak at Fs.

Fs - Speaker's free air resonant frequency. It is attributed to 4) and 5) (mass and compliance), mostly.

1), 2), and 3) are coil related, while 4), 5), and 6) are soft parts related. To change any of these would require a recone, or a different woofer.

1), 2), and 3) change with different voice coil configurations. This is why the T/S specs are slightly different for different coils in the same woofer. Changing coils will change the way the driver uses the available BL. Generally the higher ohm woofer will have a higher Fs (1 or 2 Hz), lower Qms (-5%), and dramatically higher Qes (10%).

Assuming you like your woofer and coil configuration, and only want to change the box, what are effective ways to decrease the impedance caused by 7) and 8) ??

Great explanation, even I understood it. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[tinmanchris217 10+ year member]

It's hard to get things by you, CrownVic. Any idea how to decrease impedance caused by the box?

 

[cshaw 10+ year member]

probably the most informative thread on ca.com in years. lol thanks pv audio for passing on whatever knowledge you know.

but i been meaning to read the Loudspeaker Design Cookbook for years now. i went to school for audio engineering and the week we learned about speaker systems, i was teaching most of the class, half stoners and wana be gangsta rappers in miami. i made enough money after that week installing their systems to pay my way that month lol

 

[Crownvicon28s 10+ year member]

It's hard to get things by you, CrownVic. Any idea how to decrease impedance caused by the box?

I have no idea man. I was paying attention trying to learn how. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif